After a morning meeting with a group of friends and advisers, longtime community organizer Bill Walczak told the Globe today that he will run for mayor of Boston.

A 40-year Boston resident and cofounder of the Codman Square Health Center, Walczak becomes the fifth major declared candidate in the race to replace 20-year Boston Mayor Thomas M. Menino, who announced last month that he will not seek a sixth term.

“What I care deeply about is making sure that the City of Boston continues to be a great city and making sure that all parts of the city are benefiting from that,” Walczak said.

He said in a phone interview that he sees the city’s top job as the next logical step in his career of community organizing.

Walczak, 58, has spent the bulk of the last 30 years doing community work in Dorchester, where he cofounded the Codman Square Health Center in 1975. In the ensuing years, he has raised more than $70 million for the health center and used it as a source of revitalization for the neighborhood.

He is currently president of the Codman Academy Charter Public School, which he cofounded, and vice president at Shawmut Design and Construction, where he represents the company before government and community groups. He also spent a year at the helm of the Carney Hospital, part of the Steward Health Care System.

While Walczak said he has not yet fully developed a platform, he said his vast experience and network at the neighborhood level separates him from other declared candidates and will help him lead if elected.

“I’ve certainly been involved in politics my whole life,” he said. “But this is new territory.”

Four elected officials have entered the race: Suffolk District Attorney Daniel F. Conley; city councilors John R. Connolly and Rob Consalvo; and state Representative Martin J. Walsh.

Two other candidates — Will Dorcena, cofounder of the Boston Haitian Reporter and former city council candidate, and Charles Clemons, cofounder of TOUCH 106.1 FM — have also said they are running. Several others, including a handful of other city councilors, have said publicly that they are considering a run.

“We have a really good group of candidates, they’re all really good people,” Walczak said. “It’s going to be a sprint, and I look forward to the discussions we’re going to have about the future of the city.”

Walczak said he plans to fine-tune his message and platform in the coming weeks, adding that he wants it to develop as he continues to talk to those in the communities he hopes to govern. He will have to quickly begin raising campaign funds.

Supporters, including former Boston elementary school principal Emily Shamieh, say those community roots are what makes him the right choice.

“Our meeting with him was tough, it was honest but it was supportive,” Shamieh said tonight. “If Bill can do for Boston what he did for Codman Square we’re going to all be proud to have voted for him.”